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02-18-2009, 04:14 PM
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Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
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WEST System epoxies...
Quote:
Originally Posted by Danny7
if you wet them on a table, use film plastic to sandwich them. this way you can also roll out any bubbles and excess resin. cut the whole thing with rotary cutter, and you've got perfect edges, easy to handle even when 3-4 feet long strips.
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...sell a two layer 45 degree orientation tape that works well for small applications - saves cutting and messy edges...
http://www.westmarine.com/1/1/27459-...st-system.html

__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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02-18-2009, 10:16 PM
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Join Date: Aug 2005
Location: Pasadena CA
Posts: 2,484
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Quote:
Originally Posted by Danny7
i don't see much explanation for WHY to do a 45-0-45 style.
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Quote:
Originally Posted by jsharkey
If you want to mimic a metal's strength in all directions over a big surface - e.g. a cover plate or cowling - it is common to mix 0 deg and 45 deg plies - be careful to make the plies symmetric about the mid plane though if you don't want a potato chip!
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For the windshield strip on my -6 tip-up I mixed zeros and 45s - but I don't think it matters
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To make it strong in shear, compression, and tension. Not particularly important for fairings, but if something is worth doing, it's worth doing right. I'm not a composites expert, I've never worked in a factory making plastic airplanes.... but just because Cessna does it a certain way only means they've figured out that it's acceptable. I don't know what they use for fairings, but I am absolutely sure for anything structural, they have a precise schedule for layups to assure proper strength in the proper directions... Lacking a way to determine how strong it needs to be in any given direction, I choose to make it universally strong in all directions.
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Stephen Samuelian, CFII, A&P IA, CTO
RV4 wing in Jig @ KPOC
RV7 emp built
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02-19-2009, 12:22 AM
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Join Date: May 2008
Location: central oregon
Posts: 1,089
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Quote:
Originally Posted by osxuser
To make it strong in shear, compression, and tension. Not particularly important for fairings, but if something is worth doing, it's worth doing right. I'm not a composites expert, I've never worked in a factory making plastic airplanes.... but just because Cessna does it a certain way only means they've figured out that it's acceptable. I don't know what they use for fairings, but I am absolutely sure for anything structural, they have a precise schedule for layups to assure proper strength in the proper directions... Lacking a way to determine how strong it needs to be in any given direction, I choose to make it universally strong in all directions.
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how will changing the bias orientation affect the shear strength, or for that matter compression? the way i think of composites on a metal airplane working, they primarily work in tension, until you use them in cored applications like seen on cowls. I doubt anyone is going to ask how to do that with a thread at VAF (making a cored composite anything) doesn't seem like anyone is going to make something thick enough to have a significant compressive strength.
is the shear you mention the different layers of fabric sliding against each other? how would changing the bias affect that?
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nothing special here...
Last edited by Danny7 : 02-19-2009 at 12:25 AM.
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02-19-2009, 05:47 AM
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Join Date: Nov 2006
Location: Bennington, Vermont USA
Posts: 1,301
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It's shear in the plane of the fabric - i.e. parallelogramming, skew wiffing or kitty wampusing - etc.
You are correct the layup schedule has little effect on interlaminar or ply to ply shear.
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02-19-2009, 06:14 AM
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Join Date: Jan 2005
Location: Martinsville, IN
Posts: 2,326
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Quote:
Originally Posted by Auburntsts
OK,
Silly question of the day. Once I cut a section of BID cloth off the roll on a 45 deg bias, how should I orient the subsequent layups that I cut out. Like #1, #2, or it doesn't matter. Thanks!

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For anything on an RV that is fiberglass, the strand orientation is , in all practicality, irrelevant. I can't think of a single fiberglass part that is load bearing outside of normal air pressure flows. It is best to cut your cloth 45 degrees to the selvage because this gives the strip the most strength and the most flexibility to flow around edges, etc. When cut 90 degrees or 0 degrees to the selvage, the cloth does not want to bend around corners without creating an air pocket underneath the cloth.
I wouldn't worry too much about it. If you want to change the orientation between layers, it won't hurt anything so go for it, but it's not needed for purposes of strength. Most of the stuff I see people do with fiberglass violates many of rules you should follow when building a glass airplane anyway, but since our glass is all cosmetic, it's not worth making it a big deal. Having built a Long-EZ (with the emphasis on Long, as in long time), you are schooled in the Rutan epoxy glassing techniques. As other posters have pointed out, in those airplanes strand orientation if critical because they are the load bearing structures. you must pay very close attention to number of plies, type of cloth (BID or UNI), orientation, epoxy ratio, temperature, etc. I just don't see the need for that level of intensity on our parts unless you really want to do so.
__________________
Randy Pflanzer
Greenwood, IN
www.pflanzer-aviation.com
Paid through 2043!
Lund fishing Boat, 2017, GONE FISHING
RV-12 - Completed 2014, Sold
427 Shelby Cobra - Completed 2012, Sold
F1 EVO - partially completed, Sold
F1 Rocket - Completed 2005, Sold
RV-7A - Partially completed, Sold
RV-6 - Completed 2000, Sold
Long-EZ - Completed 1987, Sold
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02-19-2009, 11:30 AM
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Join Date: Feb 2008
Location: Thousand Oaks, CA
Posts: 183
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and
If it isn't structual then it probably wont matter too much what orientation it is. Say, if your building a glove box or something. However, I try to stick with the 45 orientation on all my layups even if just making something for fun. Its easy, correct and probably looks nicer too.
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